Gas liquefaction processes have involved splitting the natural gas feed, a minor portion of the split being heat exchanged with head product to liquefy such split off natural gas. An approach is disclosed in West German Offenlegungsschrift No. 24 38 443 in which natural gas rich in nitrogen is liquefied under pressure. The natural gas is expanded and is then passed to a rectifying column for the purpose of separating the nitrogen. The resulting head product from the column rich in nitrogen is heat exchanged with a partial flow of the natural gas to be liquefied. The head product is subsequently heated to ambient temperature in heat exchange with the total flow of natural gas and with the coolants in the pre-cool and deep-cool circuits. The head product is subsequently discharged from the liquefaction installation. Such discharge may be compressed and burned in gas turbines, for example, thus helping to cover the energy requirement of the liquefaction method.
The process according to this invention liquefies the natural gas in a more efficient energy conservation manner. This is principally achieved by compressing the flash gas after heat exchange with the pre-cooled split off portion of natural gas, at least partly liquefying the compressed flash gas in heat exchange with the first and second coolant circuits and subsequently expanding and rejoining the cooled compressed flash gas with the expanded deep-cooled liquefied natural gas.